DEEP DEFECT DETECTION WITHIN THICK MULTILAYER AIRCRAFT STRUCTURES CONTAINING STEEL FASTENERS USING A GIANT-MAGNETO RESISTIVE (GMR) SENSOR

摘要

Defect detection within thick multilayer structures containing steel fasteners is a challenging task in eddy current testing due to the magnetic permeability of the fasteners and overall thickness of the structure. To address these issues, a magnet is applied to the fasteners during the inspection to reduce the noise caused by the permeability. Using a GMR sensor coupled with a lock-in amplifier to increase eddy current sensitivity, data is obtained and at low frequencies. After developing a basic signal processing algorithm, the experimental results show this system can detect second layer defects occurring 10-mm below the surface of an aluminum structure with steel fasteners.